perf: cache the key used for OTEL traces and metrics

[olavloite]

The HeaderInterceptor creates a key consisting of the database name and method name that is used for OpenTelemetry attributes and metrics. The number of unique keys is low. However, the key is constructed from the DatabaseName and method name every time, which leads to a lot of string creation:

1. The DatabaseName.toString() method is called every time. This constructs a new string.
2. The result of DatabaseName.toString() is concatenated with the methodName to create yet another string.

Instead of creating the key every time, we can cache the key values without doing the string creation and concatenation every time.

[sakthivelmanii]

nit: do you feel if there will be an improvement if we use StringBuilder instead of string concatenation?

[olavloite]

Java automatically uses StringBuilder for string concatenation, so it does not make any difference. See https://docs.oracle.com/javase/8/docs/api/java/lang/String.html

The Java language provides special support for the string concatenation operator ( + ), and for conversion of other objects to strings. String concatenation is implemented through the StringBuilder(or StringBuffer) class and its append method. String conversions are implemented through the method toString, defined by Object and inherited by all classes in Java. For additional information on string concatenation and conversion, see Gosling, Joy, and Steele, The Java Language Specification.